Voltammetric analysis of pesticides and their degradation : a case study of amitraz and its degradants

by Brimecombe, R.D.

Abstract (Summary)

Amitraz is a formamide acaricide used predominantly in the control of ectoparasites in livestock and honeybees. Amitraz hydrolysis is rapid and occurs under acidic conditions, exposure to sunlight and biodegradation by microorganisms. The main hydrolysis product of amitraz, 2,4 dimethylaniline, is recalcitrant in the environment and toxic to humans.

An electrochemical method for the determination of total amitraz residues and its final breakdown product, 2,4 dimethylaniline, in spent cattle dip, is presented. Cyclic voltammetry at a glassy carbon electrode showed the irreversible oxidation of amitraz and 2,4 dimethylaniline. A limit of detection in the range of 8.5 x 10[superscript -8] M for amitraz and 2 x 10[superscript -8] M for 2,4 dimethylaniline was determined using differential pulse voltammetry. Feasibility studies in which the effect of supporting electrolyte type and pH had on electroanalysis of amitraz and its degradants, showed that pH affects current response as well as the potential at which amitraz and its degradants are oxidised. Britton-Robinson buffer was found to be the most suitable supporting electrolyte for detection of amitraz and its degradants in terms of sensitivity and reproducibility.

Studies performed using environmental samples showed that the sensitivity and reproducibility of amitraz and 2,4 dimethylaniline analyses in spent cattle dip were comparable to analyses of amitraz and 2,4 dimethylaniline performed in Britton Robinson buffer. In addition, the feasibility of measuring amitraz and 2,4 dimethylaniline in environmental samples was assessed and compared to amitraz and 2,4 dimethylaniline analyses in Britton-Robinson buffer. Amitraz and 2,4 dimethylaniline were readily detectable in milk and honey.

Furthermore, it was elucidated that 2,4 dimethylaniline can be metabolised to 3 methylcatechol by Pseudomonas species and the proposed breakdown pathway is presented. The biological degradation of amitraz and subsequent formation of 2,4 dimethylaniline was readily monitored in spent cattle dip. The breakdown of amitraz to 2,4 dimethylaniline and then to 3-MC was monitored using cyclic voltammetry.